The effect of laser focus shift on microstructural variation of Inconel 718 produced by selective laser melting

Selective laser melting is gaining interest in the aerospace industry as a candidate for manufacturing flight hardware. With increasing popularity comes the need for rigorous qualification standards and a thorough understanding of how processing parameters can affect part quality. One such parameter is the laser focal shift, which moves the building plane relative to the focal plane of the laser. Changing the focal shift alters the power density while keeping the laser parameters constant, a novel method for tailoring the microstructures of parts made by SLM. In this study, samples were manufactured at different focal positions and their microstructures were characterized. Samples built at the focal plane had a finer microstructure than samples built away from it, a result of higher power density and a smaller spot size. Furthermore, samples in the heat-treated condition produced at the shifted locations exhibited coarser grains aligned parallel to the build direction, while those at the focal plane had a finer and more equiaxed microstructure. Differences originating from the as-built condition that remain through post processing may influence the final mechanical performance of SLM parts. Utilizing the focus shift to produce these changes presents a unique opportunity for microstructural tailoring and improved mechanical performance.